1. Field of the Invention
The present invention relates to a molten metal treatment furnace that may be used for delivering molten metal to a downstream process such as a casting machine and, more particularly, a molten metal treatment furnace with level control.
2. Description of the Prior Art
There are many known arrangements and methods for moving molten metal between furnace vessels and, further, from furnace vessels to downstream devices such as casting machines. For example, U.S. Pat. No. 3,061,298 to Yamazoe discloses an apparatus for treating molten metal in which molten metal may be transferred between two holding vessels under the force of gravity. In the arrangement disclosed by the Yamazoe patent a first or upper vessel (e.g., ladle) is positioned above a second or lower vessel. The molten metal contained in the first ladle is transferred to the second ladle under the force of gravity. A combination electromagnetic recirculation pump and heating device is located between the two vessels for recirculating molten metal from the lower vessel to the upper vessel and for heating the molten metal as it passes through the recirculation pump.
U.S. Pat. No. 3,653,426 to Groteke et al. is directed to a furnace pouring and casting system that includes a holding furnace, a molten metal charging tower, and a molten metal pouring tower. The holding furnace is in fluid communication with both the charging tower and the pouring tower. When vacuum pressure is applied within the charging and pouring towers, molten metal flows from the holding furnace to the charging and pouring towers filling these chambers. The pouring tower is further connected to the mold cavity of a casting mold. In operation, after the charging and pouring towers are filled with molten metal, the charging tower is pressurized and forces molten metal into the pouring tower. The pouring tower, in turn, charges molten metal into the mold cavity under pressure.
U.S. Pat. No. 3,771,588 to Cavanagh discloses a molten metal injection casting arrangement for injecting molten metal into a casting mold. The apparatus disclosed by the Cavanagh patent includes a melting chamber that is in fluid communication with a holding chamber. The holding chamber is in fluid communication with the mold cavity of a casting mold. The holding chamber may be pressurized to force molten metal into the mold cavity of the casting mold under pressure. The melting chamber is used to replenish the supply of molten metal in the holding chamber.
U.S. Pat. No. 3,844,453 to Eickelberg discloses an apparatus for melting and pouring molten metal that includes a first vessel connected through a lower channel with a holding and pouring vessel (e.g., second vessel). The second vessel includes an outlet passage having an outlet opening for dosing molten metal from the second vessel. The second vessel is pressurized to dose the molten metal from the vessel. The first vessel is heated by a coreless induction heater. The lower channel between the two vessels is dimensioned so that molten metal freely flows between the vessels as the pressure is changed in the second vessel. The system disclosed by the Eickelberg patent is arranged such that as the second vessel is pressurized the first vessel remains substantially full of molten metal at all times for optimum operating efficiency of the induction heater heating the first vessel.
Often, a molten metal treatment step is included during the transfer of molten metal between furnace vessels or within the furnace vessel. For example, U.S. Pat. No. 4,881,670 to Yamaoka et al. discloses a holding furnace that includes means for treating the molten metal held within the holding furnace. The holding furnace includes a holding chamber for holding the molten metal at a predetermined temperature, a metal treatment chamber for cleaning the molten metal, and a melt supplying chamber configured to supply the molten metal to a downstream process. The metal treatment chamber includes a gas lance, a thermocouple, and upper and lower limit sensors. The gas lance may be used to inject inert gas into the molten metal to remove hydrogen and other gases from the molten metal.
U.S. Pat. No. 4,844,425 to Piras et al. discloses an apparatus for degassing and filtering molten aluminum alloys. The apparatus disclosed by the Piras et al. patent includes a vessel or container body that is divided into two chambers by an internal partitioning wall. A pair of degassing units is provided in one of the chambers for degassing the molten aluminum alloy contained within the first chamber. The partitioning wall separating the container body into two chambers includes a portion formed by a porous material, such as ceramic or graphite, for filtering the molten aluminum alloy passing from the first chamber to the second chamber.
U.S. Pat. No. 4,967,827 to Campbell discloses an apparatus for melting and casting metal in which molten metal is filtered as it is transferred from a melting vessel to a casting vessel. In the apparatus disclosed by the Campbell patent, the melting and casting vessels are connected by a horizontal launder. The melting and casting vessels are enclosed by a lid that includes a plurality of electric radiant heating elements. The lid further covers the launder connecting the melting and casting vessels. A filter box is located in the launder to filter the molten metal passing through the launder to the casting vessel.
It is also known in the art to recirculate molten metal within a molten metal holding/melting furnace to increase the thermal efficiency of the furnace or for other reasons. For example, U.S. Pat. No. 5,395,094 to Areaux discloses a metal melting furnace that is divided into three chambers. The metal melting furnace includes a main chamber in which the metal is melted and two forward chambers separated from the main chamber by a wall. The metal melting furnace disclosed by the Areaux patent includes a conveying conduit connecting the two front chambers for circulation of molten metal between these chambers to improve the overall thermal efficiency of the melting operations conducted within the metal melting furnace.
U.S. Pat. No. 5,411,240 to Rapp et al. discloses a two-chamber furnace for delivering molten metal to a casting machine. The two-chambers include a storage chamber and a removal chamber. An intermediate chamber is located between the storage chamber and the removal chamber. A pump is provided in the intermediate chamber for moving the molten metal from the storage chamber to the removal chamber. An overflow pipe is provided in the intermediate chamber and is used to recirculate a portion of the molten metal flowing into the intermediate chamber back to the storage chamber.
Further, it is known in the art to include means for controlling the level of molten metal contained in a molten metal holding/melting furnace or furnace vessel. For example, U.S. Pat. No. 5,662,859 to Noda discloses a constant molten metal surface level retaining furnace. The molten metal retaining furnace disclosed by the Noda patent includes a molten metal retaining chamber for storing the molten metal. The stored molten metal is intended for delivery to an injection sleeve of a die casting machine. A molten metal surface level control device is connected to the molten metal retaining chamber and is used to control the level of a float located in the molten metal retaining chamber. By controlling the level of the float within the molten metal retaining chamber, the overall level of the molten metal within the molten metal retaining chamber may be controlled.
U.S. Pat. No. 5,700,422 to Usui et al. discloses a molten metal supply device for supplying molten metal to an injection sleeve of a die casting machine. The molten metal supply device includes a holding furnace divided into a holding chamber and a supply chamber. The supply chamber is in fluid connection with the injection sleeve through a conduit. The holding chamber includes an immersion body that may be immersed in the molten metal in the holding chamber to displace and raise the overall level of molten metal in the holding chamber. As the level of molten metal rises to a predetermined level in the holding chamber, molten metal flows from the holding chamber to the supply chamber. A laser sensor is used to monitor the level of molten metal in the holding chamber and sends signals to a control unit, which is used to control the immersion body and, hence, the molten metal level in the holding chamber.
U.S. Pat. No. 5,056,692 to Wilford et al. discloses a dispensing apparatus for molten metal that includes a vessel, a container defining a chamber, and a support structure for supporting the container such that an open end of the container is immersed in the molten metal in the vessel. A vacuum pump is connected to the container to reduce the pressure in a headspace therein to draw molten metal into the chamber. A sensor is provided to sense the level of molten metal in the vessel and is connected to a regulating unit that is operable to regulate the pressure in the headspace of the container thereby regulating the volume of liquid in the container such that the level of molten metal in the vessel is maintained at a substantially constant level as molten metal is dispensed from the vessel.
The foregoing patents disclose different methods and arrangements for moving molten metal between furnace vessels and, in some cases, disclose treating molten metal within a furnace vessel or as the molten metal passes between furnace vessels. In addition, some of the foregoing patents disclose different methods and arrangements for the level control of molten metal within a furnace vessel. However, none of the foregoing discussed patents disclose both molten metal level control at the point of use (i.e., the point at which molten metal is delivered to a downstream process) and molten metal treatment in a single system.
In view of the foregoing, it is an object of the present invention to provide a furnace that includes both molten metal level control and metal treatment in a single system. It is another object of the present invention to provide a furnace that reduces the formation of metal oxides and the entrainment of gases in the molten metal as molten metal is transferred between different areas of the furnace. Further, it is an object of the present invention to provide a furnace that is suitable for use with molten aluminum alloys and is less likely to cause metal quality issues.
The above objects are accomplished with a molten metal treatment furnace with level control in accordance with the present invention. The molten metal treatment furnace with level control may be used to deliver molten metal to a downstream process such as a dosing furnace for a casting machine or other similar process. The furnace includes a heating chamber configured to contain and heat a supply of the molten metal. A variable speed pump is in fluid communication with the heating chamber. The pump has a pump inlet connected to the heating chamber and a pump outlet. The pump is configured to pump molten metal through the furnace during operation. A degassing chamber is in fluid communication with the pump through the pump outlet. The degassing chamber includes a degassing mechanism for removing gas and impurities from the molten metal flowing through the degassing chamber under the influence of the pump. A filter chamber is located downstream and in fluid communication with the degassing chamber. The filter chamber includes a molten metal filter for filtering the molten metal flowing through the filter chamber under the influence of the pump. A dosing chamber is located downstream and in fluid communication with the filter chamber. A molten metal level sensor is located in the dosing chamber and is connected to the pump for providing a pump speed control signal to the pump. The level sensor is configured to monitor the level of the molten metal in the dosing chamber and maintain a preset level of the molten metal in the dosing chamber by controlling the speed of the pump with the pump speed control signal. A trough is connected to the dosing chamber for supplying the molten metal to the downstream process. The trough for connecting the dosing chamber to the downstream process may be heated.
The pump may be a mechanical pump having a ceramic impeller located within a ceramic housing. The filter chamber may be in fluid communication with the heating chamber through a bypass conduit such that under the influence of the pump a portion of the molten metal flowing through the filter chamber recirculates to the heating chamber through the bypass conduit. The bypass conduit may connect the filter chamber to the heating chamber upstream of the molten metal filter. The degassing mechanism may be a rotary degassing mechanism. The trough, dosing chamber, and filter chamber may be enclosed by an electrical resistance-heated lid.
The degassing chamber and the filter chamber may be provided as a combined molten metal treatment chamber. The molten metal treatment chamber may be in fluid communication with the heating chamber through a bypass conduit such that under the influence of the pump a portion of the molten metal flowing through the molten metal treatment chamber recirculates to the heating chamber through the bypass conduit. The molten metal treatment chamber may include the degassing mechanism for removing gas and impurities from the molten metal flowing through the molten metal treatment chamber under the influence of the pump. The degassing mechanism may be a rotary degassing mechanism. The molten metal treatment chamber may further include a molten metal filter for filtering the molten metal flowing through the molten metal treatment chamber under the influence of the pump. The molten metal filter may be located downstream of the degassing mechanism in the molten metal treatment chamber.
The present invention is also a method of controlling the level of molten metal in a molten metal treatment furnace as generally described hereinabove. The method may comprise the steps of: pumping the molten metal from the heating chamber to the molten metal treatment chamber; treating the molten metal in the molten metal treatment chamber; pumping the molten metal to the dosing chamber; monitoring the level of the molten metal in the dosing chamber with the level sensor; providing the pump speed control signal to the pump to control the speed of the pump and maintain a preset level of the molten metal in the dosing chamber; and dosing the molten metal from the dosing chamber to the downstream process through the trough.
The method may further include the steps of recirculating a portion of the molten metal flowing through the molten metal treatment chamber to the heating chamber; degassing the molten metal in the molten metal treatment chamber; and filtering the molten metal in the molten metal treatment chamber. The step of filtering the molten metal in the molten metal treatment chamber may be performed after the step of degassing the molten metal in the molten metal treatment chamber.